U.S. Pat. No. 6,752,094 issued to James R. Truax on Jun. 22, 2004 discloses a no-till seed planter with a wheel mounted frame having one or more transverse rock shafts each carrying a rank of seed planter assemblies. Each planter assembly includes planting equipment mounted on a planting equipment frame that is connected to one end of a mounting beam. The other end of the mounting beam is connected to a torsion joint attached to the rock shaft.
The rock shaft has a generally square cross-section shape. The torsion joint is the type having a box-like housing that is mounted diagonally on the rock shaft. Spaces formed between interior corners of housing and the flat sides of the rock shaft are filled with bar-like torsion spring elements. Rotational movement of the torsion joint housing, as when the planter assembly traverses irregular terrain, results in a return moment produced by deformation of the torsion spring elements.
The planter assemblies have the capacity for up and down movement relative to the rock shaft by virtue of the torsion joint. As the furrowing disk, depth gauge wheel and seed shoe of a planter assembly move over irregular terrain it is desirable that these pieces of equipment maintain a consistent alignment with the seed planter frame instead of following the ground irregularities. However a serial connection of the mounting beam with the planting equipment results in a rotation of the planting equipment and a deviation of the preferred alignment. The resultant angular disposition of the planting equipment during such an encounter with irregular terrain compromises planting efficiency.
Extreme rotation of the planter assembly on the rock shaft can tend to move the torsion joint housing to an over-center position and dislodge the torsion spring elements. A mechanism for limiting the permissible amount of rotation of the torsion joint housing relative to the rock shaft is desirable.